Molecular Interface Engineering and Optical Design for High-Efficiency Perovskite LEDs

Metal halide perovskite light-emitting diodes (PeLEDs) have the potential to significantly impact next-generation lighting and display technology. However, their full promise has yet to be unlocked, particularly for blue and white PeLEDs. These devices face unique challenges such as maintaining stability, achieving high efficiency, and obtaining pure color emission, especially for blue light, due to the inherent material and device-related difficulties.<br/>Our research tackles these issues through a multifaceted strategy designed to optimize the performance and efficiency of PeLEDs. We commence with interfacial engineering, introducing a self-assembled monolayer (SAM) with functional hole injection properties between the NiOx and poly(9-vinylcarbazole) hole injection layers. This approach effectively mitigates common obstacles such as weak interfacial adhesion, high interfacial trap density, and mismatched energy levels. The introduction of the SAM has successfully led to blue PeLEDs with external quantum efficiencies (EQEs) exceeding 15% and green devices with EQEs of 26.0%. In addition to enhancing efficiency, the introduction of the SAM also augments the device response speed by reducing interfacial capacitance and resistance. These advancements together pave the way for the development of more efficient, brighter, and faster responding perovskite LEDs, thereby broadening their potential applications in various fields.<br/>Furthermore, we have developed an advanced device structure that optically couples a blue PeLED with a red-emitting perovskite nanocrystal layer, leading to the creation of efficient white PeLEDs. This innovative strategy utilizes near-field effects to facilitate the extraction of trapped blue photons' optical modes to the red perovskite layer, resulting in white PeLEDs achieving EQEs over 12% - a significant advancement in white PeLED performance.